120 isn't enough for me and there's still the problem of many monsters not having an element.
Lets see...Level 5 quest is partially sleazy, level 6 is hot, level 7 is spooky, level 8 is mostly cold, level 9 you use the dictionary for, level 10 is unaligned with a few exceptions, hole in the sky is sleazy, level 11 has a combination of physical resistance, spooky and unaligned, with a few exceptions, level 12 is either sleazy or stench depending on your choice of side to support, with side quests covering all the elements (ducks), stench (larva).
So, basically, the fantasy airship and castle in the sky are your only real choke points in spell-slinging. And the airship HP ranges are 100-127 so with a half-way decent set of spell accessories you'll be two-shotting them with your best spell.
Its worth remebering, also, that sauceror spells can do double damage to any elemental type except hot.